Phil Jones, the scientist at the centre of the leaked emails scandal, said he had received death threats. Photograph: University of East Anglia

The number of Britons who believe the science of climate change has fallen over the last 12 months, according to recent polls. Although the vast majority of people still believe the planet is heating up, there has been an increase in those who believe climate change claims are exaggerated.

Public perception could have been influenced by the recent scandal of leaked emails between climate change scientists at the University of East Anglia. The emails, which appeared to encourage data to be kept from Freedom of Information requests, have been seized upon by climate change sceptics – although none of them dispute the science behind the "greenhouse effect" of gases such as carbon dioxide, which traps solar heat and warms the atmosphere.

A BBC poll, which surveyed 1,000 people, revealed that 25% of adults did not believe in global warming – a rise of 8% since a similar poll in November – and the percentage of those who thought climate change was a reality fell to 75%. Of those who believed, one in three felt climate change had been exaggerated. Only 26% of people thought climate change was "established as largely manmade".

Robert Watson, the chief scientific adviser for the Department for Environment, Food and Rural Affairs, said the results were "very disappointing". "The fact that there has been a very significant drop in the number of people that believe that we humans are changing the Earth's climate is serious," he told the BBC. According to an Ipsos poll of 1,048 people, the proportion of the public who believe in climate change has dropped from 44% to 31% in the past year.

It has been claimed most Tory MPs are sceptical about the party's focus on climate change policy. Tim Montgomerie, editor of the ConservativeHome website, said at least six shadow cabinet ministers were sceptical about the economic consequences of a low-carbon policy.

The polls come as Professor Phil Jones, the director of climate research at the University of East Anglia who is at the centre of the leaked emails scandal, said he had received death threats since the correspondence was published online. He told the Sunday Times: "There were death threats. I was shocked. People said I should go and kill myself."

Allegations about the accuracy of a 2007 report produced by the Intergovernmental Panel on Climate Change – including a claim that global warming could cut north African crop production by 50% by 2020 – could damage public perception further. The claim, used in a speech by Ban Ki-moon, the UN secretary general, has since been questioned.